Recently, along with the trend toward high speed of semiconductor devices and miniaturization of wiring patterns, Cu having higher conductivity and electromigration resistance than Al attracts attention as a material for wiring, a Cu plating seed layer, and a contact plug.
As for a method for forming a Cu film, physical vapor deposition (PVD) such as sputtering has been widely used. However, it is disadvantageous in that a step coverage becomes poor due to miniaturization of semiconductor devices.
Therefore, as for a method for forming a Cu film, there is used CVD for forming a Cu film on a substrate by a thermal decomposition reaction of a source gas containing Cu or by a reduction reaction of the source gas by a reducing gas. A Cu film (CVD-Cu film) formed by CVD has a high step coverage and a good film formation property for a thin, long and deep pattern. Thus, the Cu film has high conformability to a fine pattern and is suitable for formation of wiring, a Cu plating seed layer and a contact plug.
In the case of using a method for forming a Cu film by CVD, there is suggested a technique for using as a film-forming material (precursor) a Cu complex such as copper hexafluoroacetylacetonate trimethylvinylsilane (Cu(hfac)TMVS) or the like and thermally decomposing the Cu complex (see, e.g., Japanese Patent Application Publication No. 2000-282242).
Meanwhile, there is suggested a technique which uses, as a barrier metal or an adhesion layer of Cu, an Ru film (CVD-Ru film) formed by CVD (see Japanese Patent Application Publication No. H10-229084). The CVD-Ru film has a high step coverage and high adhesivity to a Cu film. Hence, it is suitable for the barrier metal or the adhesion layer of Cu.
However, when a monovalent diketone-based complex such as the aforementioned Cu(hfac)TMVS is used as the film-forming material of the CVD-Cu film, a by-product having a vapor pressure lower than that of the film-forming material is produced during the CVD-Cu film formation. The by-product is adsorbed on the surface of the formed film. Due to poisoning, the chemical deactivation occurs on the surface of the Ru film serving as the surface of the formed film.
Further, the adsorption of the Cu material is hindered, and the wettability between the Cu film and the Ru film is decreased. As a result, the initial nucleus density of Cu is decreased, and the surface texture of the Cu film deteriorates (rough surface patterning). Accordingly, the quality of the Cu film is decreased, and the adhesivity between the Cu film and the Ru film is decreased. These problems are generated even when a film other than the CVD-Ru film is used as a surface of a formed film.